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Direct to analysers method:
o The subject sits at rest for a minimum of 5 minutes.
. Each subject inhales to total lung capacity then performs a slow vital capacity manoeuvre to
residual volume over 30-60 seconds.
. 5 exhalations are made consecutively at 3-minute intervals.
o Nose clips are worn 5 seconds before the exhalation, and taken off between measurements.
. Measurements of NO, mouth pressure and COz are made.
. Mouth pressure is standardised to 4 mmHg by a fixed restriction.
. The sampling rate of the combined analysers was 44Omls/min.
T-piece sampling system to analysers method:
o The subject sits at rest for a minimum of 5 minutes.
. Each subject inhales to total lung capacity then performs a slow vital capacity manoeuvre to
residual volume over 30-60 seconds.
o 5 exhalations are made consecutively at 3-minute intervals.
o Nose clips are worn 5 seconds before the exhalation, and taken off between measurements.
o Measurements of NO, mouth pressure and CO2, and flow are made.
. Mouth pressure is standardised to 4 mmHg by a fixed restriction.
. Flow in the t-piece was standardised by having the subject exhale at a constant rate of
221mllmin. The subjects controlled their expiratory flow rates voluntarily observing the
rotameter bobbin level of the pneumotachograph for visual feedback.
o The sampling rate of the combined analysers including the flow was 665mls/min
Figure 6.3: Schematic diagrams of the two different types of connections: direct and t-piece
measurements
Direct:
O
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